1. Field of the Invention
This invention relates generally to aircraft transparencies and, in one particular embodiment, to a hoop load bearing polymeric aircraft window.
2. Technical Considerations
A pressurized aircraft fuselage undergoes a range of stress during normal operation due to the internal and external pressure differential and environmental conditions. This pressure differential causes the hollow aircraft fuselage to expand when the internal pressure is greater than the external pressure. As the fuselage expands, the openings in the fuselage in which the aircraft windows are held also expand or enlarge. This edge displacement at the opening can be resisted by what it is commonly known as “hoop loaded” windows. This type of window design assists in reducing the stress in the airframe by sharing some of the hoop load bearing responsibility with the fuselage. In other words, the window is completely integrated to the airframe and resists and transfers load through its structural members.
Glass is a relatively strong material and is widely used for hoop loaded bearing windows. These glass windows are held in place by fiberglass straps that are attached to the aircraft fuselage. In a desire to decrease the weight of the aircraft to increase fuel efficiency, it would be desirable to replace glass aircraft windows with lighter weight polymeric windows. However, while polymeric windows are lighter than glass windows and are easier to form into complex shapes, polymeric windows are not as mechanically strong as glass windows and are not used in hoop loaded applications. Therefore, it would be advantageous to devise an efficient interface that would allow for the use of polymeric windows in applications where hoop load bearing is desired.